1. Field of the Invention
The invention relates to control over a vehicle and, more particularly, to charging and discharging control over a battery equipped for a vehicle.
2. Description of Related Art
In recent years, hybrid vehicles and electric vehicles (hereinafter, these are collectively referred to as electromotive vehicles) are practically used. An electromotive vehicle uses a battery, an inverter and a motor that is driven by the inverter, as a power source. In such an electromotive vehicle, usually, charging and discharging of the battery are controlled so that a state quantity (hereinafter, also simply referred to as “SOC”) that indicates the state of charge of the battery falls within a constant range. It is known that, when charging and discharging are repeated within such a constant range, there occurs a deviation between an estimated SOC and an actual SOC, a decrease in charging and discharging capacity due to a so-called memory effect, degradation due to sulfation, or the like. It is known that these problems may be eliminated by bringing the battery close to a full charge or a complete discharge (so-called refreshing).
Japanese Patent Application Publication No. 2007-223462 (JP-A-2007-223462) describes a technique that reliably refreshes a battery. A control device described in JP-A-2007-223462, in a hybrid vehicle that is connectable to an external power supply, carries out refresh discharging of the battery before charging the battery from the external power supply, and charges the battery from the external power supply after the battery has been subjected to refresh discharging.
Incidentally, it is possible to estimate the full charge capacity of the battery using an SOC variation amount and accumulated current value during charging (the amount of charge flowing into the battery). That is, by multiplying the ratio of an SOC maximum value to the SOC variation amount (which is expressed by SOC maximum value/SOC variation amount, and is a value larger than 1) by the accumulated current value, it is possible to estimate the amount of charge corresponding to the SOC maximum value, that is, the full charge capacity of the battery.
If the full charge capacity is estimated by the above method, it is presumable that the estimate accuracy of the full charge capacity deteriorates when the SOC variation amount during charging cannot be sufficiently ensured. That is, the accumulated current value during charging is calculated on the basis of an output from a current sensor; however, the output from the current sensor contains an error. Therefore, when the SOC variation amount is small, the rate of amplifying the accumulated current value (=SOC maximum value/SOC variation amount) at the time of estimating the full charge capacity increases, so an error contained in the estimated full charge capacity is also amplified accordingly.
However, JP-A-2007-223462 does not describe anything about the above problem or a solution thereof.